This YouTube video discusses some of the hazards associated with the use of high pressure gas. One of the topics discussed is an incident that occurred when a facility was trying to clear a line that was blocked with a stuck pig. Fortunately no one was hurt but it was a significant near miss.
A contractor was dewatering a 10 mile section after a hydrostatic test. He was using a foam pig
that was pushed along by compressed air to displace the water. The water was being removed from a 12" bypass line. The pig got stuck somewhere in the line so they increased the pressure on the upstream side of the pig to 400 psig (28 barg). Downstream of the restriction the line was open, as shown. The differential force on the pig was almost 0.5 million pounds (2,200 kilonewtons). With that kind of force behind it the pig was going to move.
In order to catch the pig, a large front end loader was placed in front of the open pipe. The pig shot out of the pipe, flipped the loader and continued to fly approximately 150 meters in the air, destroying a wooden platform along the way.
Fortunately, all personnel had been removed from the area so there were no injuries or fatalities.